Hair coloring compositions contain various types of coloring agents, specifically, permanent, semi-permanent or direct, and temporary colorants. The permanent hair dyes are generally oxidative dyes that provide hair color that lasts about four to six weeks. These oxidative hair dyes consist of two parts; one part contains the oxidative dyes in addition to other ingredients, while the second part contains an oxidizing agent such as hydrogen peroxide. The two components are mixed immediately prior to use. The oxidizing agent oxidizes the dye precursors, which then combine to form large color molecules within the hair shaft. Although the oxidative hair dyes provide long-lasting color, the oxidizing agents they contain cause hair damage. The semi-permanent or direct hair dyes are preformed dye molecules that are applied to the hair and provide color for about six to twelve shampoos. This type of hair dye is gentler to the hair because it does not contain peroxides, but the hair color does not last as long. Temporary hair dyes are dye molecules or pigments that are too large to diffuse into the hair shaft, and therefore act on the exterior of the hair. Consequently, temporary hair dyes are generally removed after one or two shampoos.
Carbon black has been used as a temporary hair dye in hair coloring compositions, particularly for covering white or gray hair (Bogaty et al. U.S. Pat. No. 4,559,057). Additionally, carbon black has been used as a pigment in cosmetic formulations such as eye shadow, eyeliner, and mascara (Hadasch et al. U.S. Patent Application Publication No. 2002/0041854, and Grimm et al. U.S. Patent Application Publication No. 2002/0034480). Carbon black provides good covering properties, but has a weak interaction with the hair so that the adherence of the pigment to the hair is poor. Consequently, the carbon black color is readily transferred to clothing, skin, combs, brushes, and other contacting surfaces. To enhance the interaction of the carbon black pigment with hair, Igarashi et al. (U.S. Pat. No. 5,597,386) used anti-hair antibody attached to carbon black as a hair colorant. Although this method results in stronger attachment of the carbon black to hair, the antibodies are expensive and difficult to produce.
Carbon nanotubes (CNT) have been the subject of intense research since their discovery in 1991. Carbon nanotubes possess unique properties such as small size, considerable stiffness, and electrical conductivity, which make them suitable in a wide range of applications. Carbon nanotubes may be either multi-walled (MWNTs) or single-walled (SWNTs), and have diameters in the nanometer range. However, the use of carbon nanotubes as a pigment in hair coloring and cosmetic compositions has not been described.
Therefore, the need exists for a black pigment for use in hair coloring and cosmetic compositions that has enhanced interaction with hair fibers to give a more durable coloring effect.
Applicants have solved the stated problem by discovering that chemically functionalized and physically modified carbon nanotubes function as an effective black pigment in hair coloring and cosmetic compositions. The carbon nanotubes provide significant advantages for high performance hair coloring without damaging the hair. The small size of the nanotubes, typically, a few nanometers in diameter, provides a thin coating that results in a smooth feeling to the hair, while producing a volumizing effect. Additionally, the increased surface area of carbon nanotubes compared to carbon black results in enhanced contact and interaction with the hair for a longer-lasting coloring effect.